Spinneret cleaning process



United States Patent "ice 9 Claims. (Cl. 134-25 This invention relatesgenerally to the cleaning of apparatus used in the melt extrusion ofthermoplastic polymers and more particularly to a method for cleaningspinnerets that have become contaminated and clogged with thethermoplastic polymer and other substances during the production ofsynthetic filaments and yarn.

Various methods are known for cleaning spinnerets used in the meltspinning of such thermoplastic materials as polyamides, polyesters,polyurethanes, and polyolefins. In one method found fairly successful,they are cleaned by immersing the contaminated spinneret in a moltensalt bath consisting of a mixture of alkali metal nitrate and alkalimetal nitrite. In this process the temperature of the molten saltmixture ranges from 200-600" C. By using'this cleaning method, depositsof the synthetic polymer or decomposition products thereof are convertedinto gaseous products or dislodged, thus leaving the spinneret surfacesclean. 7

However, recent developments in spinning procedures have rendered thiscleaning method ineffective. In accordance with the present spinningpractice, spinnerets are subjected during spinning to a treatment withliquid polyorganosiloxanes to guarantee that the spinning process may becarried on for an extended period without interruption. This material isusually intermittently sprayed onto the spinneret surface throughout thespinning operation. Polyorganosiloxanes useful for this purpose have thefollowing formula:

wherein R is'an alkyl group, aryl group, alkaryl group, or aralkylgroup, and n is an integer greater than 1. Particularly preferredpolysiloxanes for use in this treatment are the polymethylsiloxaneshaving a viscosity ranging from 500 to 1000 centistokes at 25 C.

Although the uninterrupted spinning time of spinnerets treated withpolyorganosiloxanes is increased considerably, there are certaindisadvantages to such a treatment. The high temperatures maintainedduring the melt spinning process cause a solid deposit to form on thespinneret surfaces which must be removed from time to time to insuresatisfactory spinnability. In this connection, it has been found thatthe deposits, which originate from the polyorganosiloxanes, are notremoved by the known molten salt bath spinneret cleaning method. Such asalt bath cleaning removes the polymer deposits but leavespolyorganosiloxane residues.

It is therefore an object of this invention to provide a method forcleaning spinnerets that have been treated with a polyorganosiloxaneduring the melt spinning of polymeric materials that does not have thedisadvantages of the prior art spinneret cleaning method.

A further object of this invention is to provide a process for cleaningspinnerets that have been treated with a polyorganosiloxane during themelt spinning of polymeric materials that will remove not onlycontaminants and deposits originating with the polymeric materialextruded, but will also remove the polyorganosiloxane and decompositionproducts thereof from the spinneret.

7 Patented June 8, 1965 A still further object of this invention is toprovide a spinneret cleaning method which is simple, efficient, andinexpensive, and that will not damage the spinneret.

I These and other objects will be apparent from the'following detaileddescription.

In accordance with this invention, it has been found thatpolyorganosiloxane deposits on the spinneret can be removed utilizingthe known salt bath cleaning method if, prior to immersing thespinnerets in the alkali-metal nitrate and nitrite bath, the spinneretis subjected to a pretreatment with white mineral oil. Such apretreatment is easy to incorporate in the normal spinneret cleaningroutine customarily used. In accordance with the invention, thecontaminated spinnerets are either immersed in a white mineral oil suchas a parafiin oil orsimply smearedwith the oil,and"then soaked in amolten salt bath consisting of a mixture of alkali metal nitrate andalkali metal nitrite for asufiicient period of time to dislodgeanddecompose all foreign matter on the spinneret surfaces. Soaking time mayrange from /z'hour to 6 hours, depending on the degree of contamination.Upon withdrawal of the spinneret from the bath, all foreign deposits,including polyorganosiloxane contaminants, have been removed from thespinneret surfaces.

The purpose of the mineral oil in the inventive process is to provide asolvent action on the surface of the spinneret which aids the oxidationreaction carried out by the molten alkali salts. The only requirement asto the type of mineral oil used to produce this solvent effect duringsubmersion into molten salt bath is that the hydrocarbon mineral oilmust have a boiling point, i.e., vaporize, higher than the ambienttemperature. This is necessary to enable the spinneret to be coated withthe mineral oil when it is contacted by the molten salt bath.

For purposes of further illustration, the following examples are given.However, they are not to be construed as limiting the scope of theinvention.

Example I A 'polyamide prepared from hexamethylene .diamine' and adipicacid was'melt spun into filaments using two separate spinnerets. Duringthe spinning process, each spinneret was from time to time sprayed withpolymethylsiloxane. After the spinnerets had been used in this mannerfor two weeks, they were removed from the machine. One spinneret wasimmersed in a melt maintained at 450 C. containing about 50% by weightpotassium nitrate and 50% by weight sodium nitrite for about 5 hours.The spinneret was thereafter cooled in air and washed with warm water toremove the salt. All polyamide contaminants previously adhering to thespinneret were removed by this treatment. However, thepolymethylsiloxane deposits remained. The other spinneret after removalfrom the spinning machine was dipped in a white mineral oil bath, whoseviscosity at 20 C. was about 35 centistokes, having a specific gravityof about .87. It was thereafter immersed in a 50% by weight potassiumnitrate and 50% by weight sodium nitrite melt maintained at 450 C. forabout 5 hours and then washed with warm water to remove traces of thesalt. The spinneret was completely free from all polyamide andpolymethylsiloxane deposits.

Example II A polyamide prepared from hexamethylenediamine and adipicacid was melt spun into filaments. Two spinnerets utilized in thespinning process were both sprayed with polymethylsiloxane throughoutthe spinning. After they had been used for about three weeks, they wereremoved from the spinning apparatus. One spinneret was immersed forabout 5 hours in a melt containing 50% by weight sodium nitrate and 50%by weight sodium nitrite maintained at about 500 C. The spinneret wascooled and rinsed with warm water. No trace of the polyamide remained onthe spinneret. However, the polymethylsiloxane deposits were stillpresent. The other spinneret was dipped in a white mineral oil bathidentical with that of Example I, and then immersed for about 5 hours inthe sodium nitrate, nitrite bath under the same conditions as thespinneret which had not received the mineral oil pretreatment. After ithad been cooled and rinsed with warm water, it was found to be perfectlyclean.

As the foregoing examples clearly indicate, the method of this inventioncleans spinnerets in a practical and efficient manner without leavingany traces of polymer melt or polyorganosiloxane deposits. It'will beapparent to those skilled in the art that many widely differentembodiments of this invention may be made without departing from thespirit and scope thereof, and therefore the invention is not intended tobe limited except as indicated inthe following claims.

What is claimed is:

1. A method for cleaning apparatus used in the melt extrusion ofpolymeric material, said apparatus having been coated with apolyorganosiloxane during the extrusion process, consisting essentiallyof coating said apparatus with a white mineral oil and thereafterimmersing the apparatus in a molten salt bath consisting of a mixture ofalkali metal nitrite and alkali metal nitrate for a sufiicient period oftime to dislodge and decompose all foreign matter on the spinneretsurfaces.

2.'The process of claim 1 in which the alkali metal salts are selectedfrom the group consistingof potassium and sodium salts.

3. A method for cleaning spinnerets used in the melt extrusion ofpolymeric materials, said spinnerets being contaminated with thepolymeric material extruded together with a polyorganosiloxane appliedto the spinneret during-the extrusion operation, having the formula:

wherein R is a member selected from the group consisting of alkyl, arylalkaryl and aralkyl groups and it an integer greater than 1, consistingessentially of coating the spinnerets with a white mineral oil andthereafter immersing them in a molten salt bath consisting of a mixtureof alkali metal nitrite and alkali metal nitrate for a period of timesutlicient to dislodge and decompose all foreign matter on the spinneretsurfaces.

4. The method of claim 3 in which the alkali metal salts are selectedfrom the group consisting of sodium and potassium salts.

5. A method for cleaning spinnerets used in the melt spinning ofpolymeric materials, said spinnerets being contaminated with the saidpolymeric material and polymethylsiloxane applied during the spinningoperation consisting essentially of coating the spinneret with aparaflin oil and thereafter immersing the spinneret in a molten saltbath consisting of by weight potassium nitrate .and 50% by weight sodiumnitrite for a sufiicient period of time to dislodge and decompose allforeign matter on the spinneret surfaces.

6. The process of claim '5 in which the spinneret is immersed in thesalt bath for about 5 hours.

7. The process of claim 1 in which the salt bath comprises a mixture of50% by weight sodium nitrate and 50% by weight potassium nitrite.

8. The process of claim 5 in which the temperature of the molten saltbath is maintained at about 200-600 C.

9. A method for cleaning spinnerets used in the melt spinning of apolymeric material selected from the group consisting of polyamides,polyesters, polyurethanes and polyolefins, said spinneret beingcontaminated with said polymeric material together withpolymethylsiloxaneap- .plied during the spinning operation, consistingessentially of coating the spinneret with a paraffin oil and thereafterimmersing the spinneret for about 5 hours in a molten salt bathconsisting of 50% by weight potassium nitrate and 50% by weight sodiumnitrite, maintained at a temperature of about 450 C.

References Cited by the Examiner UNITED STATES PATENTS 2,897,104 7/59Duncan 134-29 FOREIGN PATENTS 796,770 6/58 Great Britain. 848,956 9/60Great Britain.

DONALL H. SYLVESTER, Primary Examiner.

1. A METHOD FOR CLEANINGD APPARATUS USED IN THE MELT EXTRUSION ORPOLYMERIC MATERIAL, SAID APPARATUS HAVING BEEN COATED WITH APOLYORGANOSILOXANE DURING THE EXTRUSION PROCESS, CONSISTING ESSENTIALLYOF COATING SAID APPARATUS WITH A WHITE OIL AND THEREAFTER IMMERSING THEAPPARATUS IN A MOLTEN SALT BATH CONSISTING OF A MIXTURE OF ALKALI METALNITRITE AND ALKALI METAL NITRATE FOR A SUFFICIENT PERIOD OF TIME TODISLODGE AND DECOMPOSE ALL FOREIGN MATTER ON THE SPINNERET SURFACES.